1. Field of the Invention
The present invention relates to a spreading anchor and, in particular, to a spreading anchor to be set in a bore having an undercut, and including an anchor rod having, at its one end, a cone-shaped head portion and, at its opposite end, load application means, and a sleeve surrounding the anchor rod and having, at its end adjacent to the head portion, an expansion section formed of a plurality of expansion tabs separated from each other by axially extending slots and extending from a plastic hinge in a direction, toward the head portions, with the expansion tabs expanding radially upon relative displacement of the sleeve and the head portion.
2. Description of the Prior Art
In anchoring technology, it is often necessary to form connections which are expansion pressure-free to the greatest possible extent. In particular, with small edge and axis distances, the anchoring with conventional expansion dowels or anchors can result in fracture or even in stratification of the subsoil or the ground. To prevent this, there are provided anchoring systems in which a special connection or anchoring element is form-lockingly anchored in a receiving bore. To this end, a cylindrical receiving bore is provided at a predetermined depth with an undercut. An anchoring element, which is inserted in the pre-formed bore, includes an anchor rod provided with a cone and extending through an axial through-bore of a sleeve. The sleeve is provided with expansion segments or tabs which swung out, upon relative displacement of the sleeve and the anchor rod, and engage in the undercut.
For forming an undercut, different special undercut-cutting tools are used which are equipped with circumferential cutters which are eccentrically arranged in the receiving bore and which remove, by milling or shaving, a material at a predetermined depth of the receiving bore to expand the bore to a desired dimension at this depth. Spreading anchors, which automatically form an undercut during a setting process, are also known. To this end, the radially expanding expansion tabs are provided with cutters which chisel an undercut during a pure axial setting process or which mill the undercut when the sleeve is rotated upon being axially displaced. An example of the later-mentioned type of a spreading anchor is disclosed in U.S. Pat. No. 4,702,654. The known undercut-selfcutting spreading anchor has an anchor rod with a core and a sleeve with expansion tabs which is axially displaced relative to the anchor rod. The expansion tabs extend from a plastic hinge in a direction toward the core, which is provided at the front end of the anchor rod, and are equipped with cutting inserts provided on outer surfaces of the expansion tabs. During mounting or setting of this spreading anchor, the anchor rod is supported on the bottom of the receiving bore. The sleeve is rotatably displaced over the core, and the expansion tabs radially expand, with the cutting inserts forming an undercut in the wall of the receiving bore.
The known spreading anchors, which are designed for setting in a bore with and undercut such as, e.g., disclosed in U.S. Pat. No. 4,702,654, include sleeves with radially expanding expansion tabs which have, in a side view, a substantially rectangular contour. After the setting process, the radially expanded expansion tabs cover only a portion of an undercut surface formed in a bore of a structural component. This is particularly noticeable with the free front edges of the expansion tabs, which extend at a substantially right angle and which leave free a larger portion of the circular contour of the undercut. The front edges of the expansion tabs, which extend substantially perpendicular to the radius of the undercut and engage the outer contour of the undercut with their free corners. Therefore, a relatively large portion of the undercut remains unused for load transmission. Also, at the opposite end of the expansion tabs, in the region of the plastic hinge, there exist an incongruity between the abutting surface of the expansion tabs and the undercut surface of the undercut in an expanded position of the expansion tabs. Because of only partial use of the undercut surface, the achievable load values are smaller than those which were possible based on radial expansion of the undercut.
Accordingly, an object of the present invention is to eliminate the drawbacks of the know spreading anchor. Another object of the present invention is to provide a spreading anchor which would insure a better use of the available undercut surface of the undercut for load transmission and which would permit, thereby, to achieve better load values.